2.1. Cell lines and media
Chinese hamster ovary cells for suspension culture (CHO-S) were purchased from Gibco, USA. CHO 1-15 cells (CRL-9606) were purchased from ATCC, USA. Ham’s F-12 (Wako Pure Chemical Corporation, Japan) with 10% FBS (Thermo Fisher Scientific, USA) and CHO-S-SFM II (Thermo Fisher Scientific, USA) were used for culture of CHO-S and CHO 1-15 cells, respectively. All media were supplemented with penicillin/streptomycin solution (Nacalai Tesque, Japan). Cells were maintained in CO2 incubator (Panasonic, Japan), at 37 °C with air containing 5% CO2. Cell number was measured by Cell Counter TC20 (Bio-Rad, USA) after staining cells with 0.5% trypan blue solution (Nacalai Tesque, Japan).